Yushi Oishi

Nanomosaic : Formation of Nanodomains Confined in a Two-Dimensional Molecular Plane

Atomic force microscopy observations of a (hydrocarbon guanidinium/fluorocarbon carboxylic acid) mixed monolayer revealed that a nanoscopic phase-separated structure was formed by a combination of attractive interaction between the oppositely charged head groups and repulsive phase separation of the hydrocarbon and fluorocarbon chains.

Promotion of cell adhesion by low-molecular-weight hydrogel by Lys based amphiphile

Hydrogels formed by low-molecular hydrogelators have been used as anti-microbial agents and cell-attachment materials. However the biomedical application of low-molecular gelators is slowly progressing compared to the hydrogels formed by polymer hydrogelator that is applied to biomedical application such as tissue engineering and biomedical regions. To obtain a simple molecular model for potent and prospective usage of low-molecular hydrogelators, we designed a Lys-based hydrogelator which was mimic to the poly cationic poly-l-lysine that promotes cells to attach to a plastic plate nonspecifically. The gel-coating led to cause 10-fold cell attachment compared to no-coating well. Also five-time cells were attached to the well compared to the poly-l-lysine coating. From the competitive assay, these hydrogels could interact with cells through electrostatic interaction between positive charge from -NH3(+) in the hydrogelator and negative charge from substances on the cell surface such as glycosaminoglycans. This strong adhesive ability can be useful for the tissue engineering and molecular glue regions using low-molecular hydrogels in the future.

Atomic force microscopic observation of a dialkylmelamine monolayer on barbituric acid

A monolayer of 2-amino-4,6-di(dodecylamino)-1,3,5-triazine 1 transferred from barbituric acid solution onto a mica plate is observed by atomic force microscopy (AFM) to show regularly arrayed terminal methyl groups of 1 as a result of hydrogen-bond networking.

Non-equilibrium characteristics of a two-dimensional ultrathin film prepared by the water casting method

Abstract A two-dimensional ultrathin film was defined as being a film thinner than the dimension of an unperturbed Gaussian chain in the three-dimensional state. The segment density of an unperturbed chain in equilibrium in the two-dimensional solid state was investigated using a Monte-Carlo simulation. When the film thickness exceeds 30% of twice the radius of gyration of a three-dimensional unperturbed chain, the segment density is not particularly high in comparison with the three-dimensional state. This means that a polymer chain will behave as a two-dimensional unperturbed chain in the equilibrium state of a two-dimensional ultrathin film, as in a three-dimensional solid state. Therefore, the excess expansion of a polymer chain in a two-dimensional ultrathin polystyrene film with a thickness comparable to twice the radius of gyration of a three-dimensional unperturbed chain might arise from non-equilibrium characteristics. In addition, the relaxation behaviour of a two-dimensional ultrathin film of a styrenebutadienestyrene (SBS) triblock copolymer was investigated by transmission electron microscopy. The two-dimensional ultrathin SBS film contracted and decomposed into two phases (polystyrene and polybutadiene) from the one phase right after the film preparation. This indicates that the two-dimensional ultrathin film was in a distinct non-equilibrium state right after spreading a solution on the water surface.

Morphology and molecular orientation and structure of Langmuir–Blodgett films of chlorophyll a studied by atomic force microscopy and UV–VIS and IR spectroscopies

Atomic force microscopy (AFM), scanning electron microscopy (SEM) and UV–VIS absorption and IR spectroscopies have been used to investigate the morphological and molecular structure of Langmuir–Blodgett (LB) films of the title compound (Chl-a). The AFM and SEM measurements reveal that the surface of the LB films are very smooth and consist of rigid and condensed monolayers. The tilt angle of the chlorin plane in a six-monolayer LB film of Chl-a has been calculated to be 35° between the normal of the chlorin plane and the substrate normal and 44° between the dipping direction and projection of the normal of the chlorin plane, from measurements of its polarized UV–VIS spectra. Band frequencies in the 1750–1400 cm −1 region of the IR spectra of one-, six- and ten-monolayer (ML) LB films of Chl-a suggest that Chl-a exists in a five-coordinated monomer in the films, irrespective of the number of monolayers. Comparison of IR transmission and reflection–absorption spectra of 6 ML LB films of Chl-a indicates that the chlorin plane and the ester and keto CO groups are tilted considerably with respect to the surface normal. LB films of pheophytine a (Phe-a) have also been studied for comparison. Comparison of the UV–VIS and IR spectra of the LB films of Chl-a and Phe-a show that pheophytinization occurs little in the LB films of Chl-a. High-performance liquid chromatography (HPLC) examination has supported this conclusion. All the experiments carried out in the present study suggest that Chl-a molecules in the LB films are oriented in an orderly manner with face-to-face packing of the chlorin rings.

Direct observation of defect-diminished fatty acid monolayers and their optical applications

Abstract The aggregation structure of fatty acid monolayers on the water surface have been classified with respect to thermal ( T sp , T αc , T m ) and chemical (the degree of ionic dissociation of hydrophilic group) factors. In the case of amphiphiles with a non-ionic hydrophilic group, at T sp below T m , the monolayer is in a crystalline phase which is designated “the crystalline monolayer”. The crystalline monolayer is further classified into “the fusing-oriented crystalline monolayer” and “the randomly assembled crystalline monolayer” at T sp below and above T αc , respectively. At T sp above T m , the monolayer is in an amorphous phase which is designated “the amorphous monolayer”. In the case of amphiphiles with an ionic hydrophilic group, at T sp below T m , amphiphile molecules form “the compressing crystallized monolayer”, and T sp above T m , the monolayer is not crystallized by compression. Molecular-resolution images of molecules in the monolayers were successfully observed with an atomic force microscope (AFM) for the first time. A high mechanical stability of the monolayer is inevitably required for the non-destructive AFM observation of the fatty acid monolayer. For the preparation of the mechanically stable monolayer, the continuous compression method up to a low surface pressure and the multi-step creep method were used. Further, the Langmuir-Blodgett (LB) films with a homogeneous surface morphology could be constructed by the mechanically stable monolayers, and the morphological homogeneity was necessary for the construction of low-propagation loss LB film optical waveguides.

Classification for molecular aggregation structure of monolayers on the water surface

Abstract The melting temperature, T m , and the crystalline relaxation temperature, Tα c , of palmitic acid and dipalmitoyl phosphatidylcholine monolayers on the water surface were evaluated by combination of two kinds of measurements: first, the subphase temperature, T sp , dependence of the monolayer modulus based on the surface pressure-area (π- A ) isotherm and second, the T sp dependence of the electron diffraction, ED patterns of their monolayers. On the basis of their characteristic temperatures of the monolayers, the aggregation structure of the monolayers which were transferred onto a hydrophilic SiO substrate at various surface pressures and T sp s was investigated by means of transmission electron microscopy. The π- A isotherm for the fatty acid monolayer on the pure water surface represented the aggregating process of isolated domains grown right after spreading a solution on the pure water surface. The fatty acid monolayer on the pure water surface was classified into a crystalline monolayer ( T sp T m ) and an amorphous one ( T sp > T m ). The crystalline monolayer was further classified into two types; crystalline domains were aligned along their crystallographic axes owing to an induced sintering at the interfacial region among monolayer domains by surface compression ( T sp Tα c ), while not for T sp > Tα c . In the case of the phospholipid monolayer, the monolayer was classified into a compressing crystallized monolayer ( T sp T m ) and an amorphous one ( T sp > T m ). The compressing crystallized monolayer is a monolayer in which crystallization was gradually induced at plateau region on the π- A isotherm by compression. Electron diffraction studies of arachidic acid monolayers in different dissociated states of hydrophilic groups revealed that formation of the compressing crystallized monolayer was attributed to an electrostatic repulsion among ionic hydrophilic groups. It was concluded that the aggregation structure of monolayers on the water surface was systematically classified into ‘the crystalline monolayer’, ‘the amorphous monolayer’ and ‘the compressing crystallized monolayer’, with respect to thermal and chemical (intermolecular repulsive) factors.

Control of molecular ordering in guanidinium-functionalized monolayer by carboxylate template molecules

Electron diffraction studies of a [(dioctadecyl)carbamoylmethyl]guanidinium toluene-p-sulfonate (DG) monolayer reveal that the regularity of the molecular arrangement and the size of crystalline domains are controlled through binding of aqueous α,ω-dicarboxylates with various spacer lengths.

Nanotribology of behenic acid monolayer and its aggregation state

Abstract The tribological properties of behenic acid monolayers in CS and L 2 phases were investigated on the basis of scanning probe microscopic observations. The lateral (friction) force of the monolayers in CS and L 2 phases increased consistently with applied force. The increment in CS phase comes from an increase in contact area between a probe and the monolayer owing to elastic deformation, while that in L 2 phase does from not only increase in contact area owing to plastic deformation but wear of the monolayer. The lateral force of the monolayer in CS phase was independent of the scan velocity. On the other hand, the monolayer in L 2 phase exhibited the scan velocity dependence of the lateral force. The difference in tribological properties of the monolayer is attributable to the static mechanical properties of elasticity and plasticity which are governed by the molecular packing in monolayer.

A novel preparation method of lead-based layered perovskite Langmuir films with a negligible amount of PbBr2

The addition of halide salts into the subphase has caused formation of the layered perovskite structure in a Langmuir monolayer on the subphase containing lead bromide at a concentration three orders of magnitude lower than that in the conventional methods.